Fluval U-Series Internal Aquarium Filters

Discover key features, filter process and beneficial maintenance tips on Fluval’s U Internal Filter Series.

To learn more, visit: http://www.fluvalaquatics.com/ca/freshwater/aquarium-filtration/series/u-series/


Jennifer's Usborne Bookcase says:

I just set up a new 20 g tall. I chose a Fluval U3 and it is currently cycling, fishless. I have gravel substrate, no sand. A mixture of live plants and artificial. WIthin days I started getting hard spray from the Fluval and tons of fine bubbles. I have tinkered with the adjustments endlessly and nothing has helped. Is this a defective filter? There is no gunk, because the tank and filter is new.. everything is clear and clean. This is my second tank and I have never seen this before.

Steve says:

274 posts
Posted 05 May 2012 – 03:48 PM
I’ve had a couple fish get stuck behind the U4- a paradise fish (3 times now- funnily enough he never seems stressed to get stuck there-stupid thing), 2 rosy barbs, a white cloud and a guppy. I put some sponge behind it but the white cloud still managed to get wedge there. Luckily all but the guppy survived. (Just one of the many posts online regarding this issue) maybe a rethink on the bracket design is in order,like I said its a good filter apart from this problem.

Ahmad Alhelal says:

I have a 75 gallon tank, will the U4 be a good choice, since I don’t like using a canister filter?

mcallisters views says:

Tried them last year I got the u4 and hated it I had to manually start the impeller every time I done a water change on my tank, the bracket was terrible and the carbon pads clogged too soon (money making pads).

Kurt Hanson says:

I have a Fluval U4 in a 40 gallon acrylic tank. it is just not doing a very good job keeping the water clean. My fish are thriving, but there’s a lot of debris in the water. I wash out the foam and charcoal pads in aquarium water every water change 4 times a month. I change the charcoal pads twice a month. Should I install a canister filter like the Fluval 206? 

Steve says:

Hi Fluval, unfortunately I can assure you it is possible as I have two of these in my tank and have had numerous tetras etc get trapped,if you google it you will see that I’m not the only one it’s happened to.As soon as I get the money together il be using a 406 external and ditching the u4s.Shame as they do a good job apart from this issue.

Steve says:

Yeah great filter,as long as you dont mind your fish getting stuck behind them in the awful death trap bracket on the back of it.

Roger Dedham says:

I just purchased my U4 and I’m amazed at how much water it can filter. My question relates to the biomax that came with it. Out of the box it doesn’t come with enough of it. Was this intentional by Fluval or are we allowed to add more to bio cartridge as there is lots of extra room.

1992pattrow says:

I use these filters for all my tanks under 40 gallons and i love them. Very quiet and you have many flow options due to the spray bar. They are very sensitive to water level and will start to suck in air if you let the later levels drop to much but they are amzing filters.

Craig Barrett says:

can the u4 be set horizontally as well as vertically in the tank?

is there any advantages or disadvantages in how and where it is placed?

Adhithyan Mukundan says:

Will the filters help to supply oxygen to the aquarium ?
I don’t have an air pump so I’m confused that should I buy one or my filter is capable to supply oxygen, so please help me

matthew o'dea says:

hi iv just bought a seconden hand u3 filter but theres 2 suckon pads missing and the venturas also missing the lid was broken iv found a site where I can buy the media and  new lid but can u buy the ventura n suckon pads s replacement parts these are great filters but parts all off very easily uv to be carefull I also bought anew u2 and the things that you can put onto the nozzels cum off far to esty maybe fluval can improve these parts in the furture if u done that uv have a perfact internal

majooismajor says:

how is u2 for a 20g betta tank ? Is the middle spray hose soft enough not to disturb the betta’s water ?

deano91209 says:

switching over to the fluval u4 filter at the  weekend from  a shitty aqauel filter

ThePatatonga says:

Hello everybody, more than a month ago I decided to have a Fluval U4. And most recently I have problems with the water outlet. I have in the beginning the carbon changed and put cotton on the outer layers. So, about one week ago I decided to renew the old cotton with new one. This I did, because there were coming strange sounds like whistling with lots of little bubbles out of the Fluval. And it was well done, cause all cotton was soacked with filth. This morning (a week later) I woke up and soon I heard a similar noise. I wonder what is the problem of my Fluval? Can it be again the filth… I just had NO3 too high and wouldnt like 2 change the cotton now. Does anybody have similar experiences?
It would be great if you help. My tank contains about 29 gallons. There are plenty plants. Inside swimming 20 Amber tetras and six corydoras and 9 otos. Thanks a lot for reading and helping. I’d really loved to have my U4 *really* easy to be maintained…

Setesh says:

I have an indoor pond like setup at home for my small shallow water turtles and guppies. Since it sits on the ground a canister filter is not really an option, I wonder if two of these could manage to keep it clean? Currently there is about 80 gallons of water, eventually I’ll add more water to cap at around 105gallons. I must add I destroyed two pumps in the last 3 months, shallow water (8″) and sand combo, but there was only a sponge on those and they did sit directly on the sand, I plan to sit these filters on lava rocks.

J Azizi says:

hi, i have a 54 letter (15G) fish tank, i have 8 goldfish in, and im doing 25 to 50% water change twice a week, and doing some vacuum cleaner as well, but i have cloudy water and i was recommended a power full filter so i chose fluval u2 ,, is it gone help me to get crystal clean water ,if not , help me pls any recommendation please , thank u..

Günter TV says:

the u2, u3 and u4 are great but the u1 is total shit.
but i once got a guppy stuck behinde the u2

D Leal says:

is this the equivalent to the marineland magniflow water polisher? or is this only to be used as filtration?

Lynne R says:

Does Fluval make a submersible filter that has the option of a fountain-style return? I want to use one in a small 20 gallon patio pond. Thanks!

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